NSF Funds Earthquake Simulations

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Solving the Inverse Problem
As a first test for the extreme computational challenge of
the inverse problem, the Quake Group chose a 2D shear-wave
velocity distribution (top) in a 35 km x 20 km cross-section
of the LA Basin model as a synthetic target. Starting with
ground-motion measurements on the surface (64 points
distributed evenly), the inverse algorithm (with a 257 x 257
grid) arrived at material properties for the cross-section
that gave a velocity distribution (bottom) in close match to
the target.

PITTSBURGH, October 10, 2003 
The Quake Group, a
large collaborative research team led by Jacobo Bielak, Omar
Ghattas and David O'Hallaron of Carnegie Mellon University, has
received $1.9 million from the National Science Foundation to
continue its work in high-fidelity earthquake modeling. This grant,
through the NSF Information
Technology Research program, will support the Quake Group and
PSC collaborators in developing a 3D seismic "inverse" model that
can determine subsurface geology by working backward from seismic
measurements on the surface.

In recent
computations with LeMieux, PSC's terascale system, the Quake
Group simulated the 1994 Northridge earthquake at double the
frequency of prior earthquake models. For work on the inverse
problem, Ghattas and his former students Volkan Akcelik and George
Biros won the Best Technical Paper Award last year at
Supercomputing 2002. Their inverse wave-propagation algorithm
exploits parallel systems like LeMieux, which they recently used to
solve a test case in two dimensions, demonstrating the
viability of their inverse approach.

In future work with LeMieux, they plan to extend the inverse
simulations to 3D. "The inverse problem is orders of magnitude more
difficult than the forward problem," says Ghattas. "Large parallel
systems and powerful algorithms are crucial."